The field of the invention generally relates to top loading automatic clothes washers, and more particularly relates to a method and apparatus for spinning and draining such clothes washers.
As is well known, a top loading automatic clothes washer typically sequences through various cycles to accomplish automatic washing of a clothes load. In particular, after clothes are loaded into an automatic washing machine, an operator actuable control is used to initiate a wash sequence that starts by filling the wash tub with water. Detergent is generally added before or during the filling process. Following an agitate cycle, the clothes are spun dry by draining the water and spinning an inner perforate spin basket which holds the clothes. Then, following a rinse cycle, the clothes are spun dry again. In a spin cycle of one prior art washing machine, the drain pump and the drive for the spin basket are initiated simultaneously. That is, water is pumped from the wash tub at the same time that the inner perforate spin basket is spinning. One problem with this arrangement is that the clothes are centrifuged against the walls of the spin basket, and much of the water exits the spin basket horizontally through the clothes thereby depositing lint on the clothes. Simply stated, the clothes act as a lint filter and undesirably collect lint.
In another prior art clothes washer, the drain pump is activated first, and the drive for the spin basket is only activated after the water has been pumped down. This arrangement has been referred to as a "neutral drain" system because the drive for the spin basket is in neutral while the water is being drained from the wash tub. The above described problem of collecting lint on the clothes is improved with a neutral drain system. That is, there is no spinning during the initial pump down, so the water is not driven horizontally through the clothes. Further, this arrangement has the advantage of not requiring a relatively large pump. More specifically, the flow rate of the drain pump can be relatively low because the pumping down of the water is independent of spinning, so the time to empty the wash tub is not critical. However, one remaining drawback is that the drain pump may tend to cavitate after the spin basket starts to spin. In particular, as the water is extracted from the clothes by spinning, a relatively high concentration of suds tends to be generated. The suds are compressible, and can not be effectively pumped by the drain pump. That is, the pump cavitates, or circulates the same compressible fluid, thereby reducing the net outflow.
One prior art approach for reducing cavitation is to pulse or intermittently activate the drive to the spin basket during an initial stage of a spin cycle. Suds are generated faster at higher spin speeds, and the pulsing prevents the spin basket from getting up to a maximum spin speed until most of the liquid has been extracted from the clothes. As a result, the generation of suds is reduced. However, cavitation is still a problem, and it reduces the effectiveness and efficiency of a given pump.